Burner assembly for heating a screed plate of a paving machine

Abstract

A burner assembly for heating a screed plate of a screed assembly connected to a frame of a paving machine. The screed assembly includes a heating chamber adjacent to the screed plate. The burner assembly includes a blower that moves air into the heating chamber, and a fuel injection system including a fuel valve. The fuel injection system introduces fuel to the heating chamber. The burner assembly further includes an igniter that ignites the fuel to produce a flame, a thermocouple positioned within an expected flame path, and a controller. The thermocouple generates a thermocouple voltage having a relationship to a temperature surrounding a junction of the thermocouple, and the controller operates the fuel valve based in part on the thermocouple voltage.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to burner assemblies for paving machines, and particularly a burner assembly including a thermocouple located within an expected flame path of the burner assembly.

[0002] Paving machines receive a paving material (e.g., asphalt), and lay a uniform layer of the material on a base or bed. In general, a paving machine includes a vessel or hopper that receives the paving material, and a conveyor that moves the paving material from the hopper to a distributing auger. The distributing auger distributes the paving material on to the bed. A typical paving machine also includes a screed assembly having a heating chamber, a screed plate, tie bars, and a burner assembly that heats the heating chamber. The tie bars move around a pivot allowing the screed plate to contact the paving material. The screed plate receives thermal energy from the burner assembly, and shapes the paving material into a desired form. The burner assembly heats the screed plate to an optimum temperature to facilitate shaping of the paving material. If the screed plate temperature is too low, the paving material may adhere to the screed plate, or may be too hard to work. If the screed plate temperature is too high, the screed plate may warp, or the paving material may be damaged.

[0003] As a safety feature, some known fuel burner assemblies included an optical sensor that determines whether a flame is present. The optical sensor generates an output signal when a flame is absent, and when fuel is being provided to the heating chamber. The output signal is fed to a fuel valve, causing the valve to close, and preventing a fuel introduction. One problem with optical sensors is that soot and other particles often stick to the photoelectric cells of the sensor. This results in the optical sensor becoming “blinded.” A second problem with optical sensors is that the sensor may accidentally sense extraneous light signifying a flame when no flame is being produced.

SUMMARY OF THE INVENTION

[0004] The invention provides a burner assembly for heating a screed plate of a screed assembly connected to a frame of a paving machine. The screed assembly includes a heating chamber adjacent to the screed plate. The burner assembly includes a blower that moves air into the heating chamber, and a fuel injection system that has a fuel valve. The fuel injection system introduces fuel to the heating chamber. The burner assembly also includes an igniter that ignites the fuel to produce a flame, a thermocouple positioned within an expected flame path, and a controller. The thermocouple generates a thermocouple voltage having a relationship to a temperature surrounding a junction of the thermocouple, and the controller operates the fuel valve based in part on the thermocouple voltage.

[0005] The burner assembly uses a thermocouple for sensing the flame. The thermocouple is positioned substantially within the expected flame path, and generates a signal functionally related to a sensed temperature. The generated signal is then analyzed to determine whether a flame exists. Unlike the optical sensor used with known burner assemblies, extraneous light or lack of light due to particle buildup does not effect the thermocouple.

[0006] In some embodiments of the invention, the burner assembly also includes a unique temperature sensing circuit. The temperature sensing circuit includes an amplifier, and a thermocouple that produces a thermocouple voltage. The amplifier includes a first input pin that receives the thermocouple voltage, and a first power pin that receives a current. The amplifier controls an amplitude of the current provided to the amplifier based on a relationship to the thermocouple voltage. The temperature sensing circuit also includes a resistor having a first end connected to a power supply, and a second end connected to the amplifier at the first power pin. The resistor receives the current, and develops a first voltage at the second end.

[0007] In another embodiment the invention provides a method of controlling a burner assembly connected to a frame of a paving machine. The method includes providing a thermocouple having a thermocouple junction, positioning the thermocouple junction within an expected flame path, generating a signal being functionally related to a temperature surrounding the thermocouple junction, analyzing the thermocouple voltage, and generating an output when the analyzed signal signifies a non-lit fuel condition.

[0008] Other features and advantages of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings:

[0010] FIG. 1 illustrates a side view of a paving machine of the invention.

[0011] FIG. 2 illustrates a perspective view of a burner assembly used in connection with the paving machine of FIG. 1.

[0012] FIG. 3 illustrates a partial planer and schematic view of the burner and screed assemblies used in connection with the paving machine of FIG. 1.

[0013] FIG. 4 illustrates a block diagram of the burner assembly.

[0014] FIG. 5 is an electrical schematic of first and second signal converters used in the burner assembly.

[0015] FIG. 6 is a flow chart showing a method of sampling a conditioned signal.

[0016] FIG. 7 is a flow chart showing a method of analyzing the conditioned signal.

DETAILED DESCRIPTION

[0017] Before any embodiments of the invention are explained, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. In the figures, common elements are designated with the same reference numerals.

[0018] A paving machine 100 is shown in FIG. 1. The paving machine includes a frame 105, a plurality of wheels 110, a vessel or hopper 115, a conveyor 120, a distributing auger (not shown), a screed assembly 125, and one or more burner assemblies 130. The wheels 110 rotate with respect to the frame 105, and support the frame 105 above a bed 135. The hopper 115 is connected to the frame 105, and holds a paving material (e.g., asphalt, etc.) used for creating a layer 140. The conveyor 120 is connected to the frame 105, and moves the paving material from the hopper 115 to the distributing auger. The distributing auger is connected to the frame 105, and distributes the paving material on to the bed 135. The floating screed assembly 125 rotates around a pivot 145 such that a screed plate 150 may contact the distributed paving material. The screed plate 150 works or forms the distributed paving material into a desired shape or form. The screed assembly 125 also includes one or more heating chambers 155 heated by the one or more burner assembles 130.

[0019] The one or more burner assemblies 130 are connected to the frame 105, and are operable to heat one or more heating chamber 155 with a flame 160 (FIG. 3), respectively. The flame 160 has an expected flame path 162. Although multiple burner assemblies may be used, to simplify the description herein, only one burner assembly 130 and one chamber 155 will be described.

[0020] As shown in FIGS. 2-4, the burner assembly 130 includes a blower 200, such as a fan, that moves air into the heating chamber 155, and a fuel injection system 205 that provides fuel into the heating chamber 155. The fuel injection system includes a fuel valve 210, and a fuel injector 215. The fuel valve 210 has a closed state and an open state, and controls the amount of fuel provided to the fuel injector 215. The fuel injector 215 controllably disperses or introduces fuel to the heating chamber 155. The blower 200 and the fuel injection system 205 create an air/fuel mixture. The burner assembly 130 further includes an igniter 220 that ignites the air/fuel mixture resulting in a flame 160 that provides thermal energy. As is known in the art, the intensity and quality of the flame 160 is determined by the amount of fuel being passed through the fuel valve 210, and the amount of air (specifically O2) being moved by the blower 200. The heating chamber 155 includes a flame deflector 225 that directs the flame away from the screed plate 150. This avoids direct heating of the screed plate 150, which may damage the screed plate 150. Directing the flame into the heating chamber 155 results in more uniform heating of the screed plate 150.

[0021] The burner assembly 130 also includes a thermocouple 230, a first signal converter 235, a controller 240, a chamber temperature sensor 245, an input device 250, and an output device 255. The thermocouple 230 is placed within the heating chamber 155, and is substantially within the expected flame path 162. For the embodiment described herein, the thermocouple 235 is a K-type thermocouple; however, other thermocouples may be used with the invention. The thermocouple 235 includes a junction 260, and generates a small voltage (referred to as a “thermocouple” voltage) that varies as the temperature of the junction 260 (referred to as a “junction” temperature) varies. The junction temperature is substantially identical to the temperature surrounding the junction. If junction 260 is within the flame 160, then the junction temperature is substantially identical to the temperature of the flame 160. Consequently, the thermocouple 230 creates a thermocouple voltage signal functionally related to the temperature of the flame when the air/fuel mixture is ignited or lit.

[0022] For the embodiment shown, the thermocouple voltage signal is provided to the first signal converter 235. As is discussed in further detail below, the first signal converter 235 receives a current from the controller 240, and controls the amplitude of the current based on the thermocouple voltage. More specifically, the first signal converter 235 superimposes the signal created by the thermocouple voltage on to a current provided by the controller 240.

[0023] The second temperature sensor 245 measures an ambient temperature of the heating chamber 155 a position away from the flame 160, and generates a chamber temperature signal. The ambient temperature of the chamber 155 is functionally related to the temperature of the screed plate 150. The output signal of the second temperature sensor 245 is provided to the controller 245 for analysis.

[0024] In general, the controller 240 provides a current to the first signal conditioner 235, receives the superimposed signal generated by the thermocouple 230, receives the chamber temperature signal from the chamber temperature sensor 255, receives one or more inputs from the input device 250, analyzes the various inputs, and controls the blower 200, the fuel valve 210, igniter 220, and output device 255 in response to the analysis of the inputs.

[0025] As schematically shown in FIG. 4, the controller 240 includes a second signal converter 265, a processing unit 270, and a memory 275. The second signal converter 265 (discussed in detail below) converts the superimposed signal into a conditioned signal. The conditioned signal has a voltage range (e.g., zero VDC to 5 VDC) and is provided to the processing unit 270.

[0026] Although the first signal converter 235 is external to the controller 240 and the second signal converter 265 is internal to the controller 240, other arrangements are envisioned. For example, the first and second signal converters 235 and 265 may be combined into a single signal conditioner external to the controller. Similarly, the first and second signal conditioners 235 and 265 may be combined into one circuit internal to the controller 240. In addition, other signal conditioners are possible for some aspects of the invention. For example, a signal conditioner having a cold-junction reference may be used to receive the thermocouple voltage, and to generate the conditioned signal provided to the processing unit for analysis.

[0027] Exemplary first and second signal converters 235 and 265 are schematically shown in FIG. 5. As shown in FIG. 5, the first signal converter 235 includes first and second input terminals 300 and 305, an amplifier 306, resistors R1 and R2, capacitor C1, and first and second output terminals 310 and 315. The thermocouple 230 is connected to the amplifier 306 via the first and second input terminals 300 and 305. The amplifier 306 includes two input pins 307 and 308, two power pins 309 and 310, and output pin 311. For the embodiment shown, a first end of the thermocouple 230 is connected to input pin 307 and a second end of the resistor R2. The second end of the thermocouple 230 is connected to ground. The second end of resistor R2 is also connected to ground. The output of amplifier 306 is connected to a first end of resistor R1, and to the input terminal 308 of amplifier 306. The second end of resistor R1 is connected to ground. The power pin 309 is connected to the first output terminal 310, and the power pin 310 is connected to ground. The first and second output terminals 310 and 315 are connected to third and fourth input terminals 320 and 325 of the second signal converter 265. Capacitor C1 is connected across the first and second outputs of the first signal converter, and provides filtering of the output signal.

[0028] During operation of the paving machine 100, the thermocouple voltage is provided to the first signal converter 235 at the first and second input terminals 300 and 305. The thermocouple voltage, which is referenced to ground, is provided to input pin 307. The amplifier 306 receives power at power pin 309 from the controller 240. The power received from the controller 240 powers the amplifier 306 such that the power consumed by the amplifier 306 is functionally related to the thermocouple voltage applied to the amplifier 306. This results in a varying current being supplied to the amplifier 306, where the amplitude of the current is functionally related (e.g., proportional) to the thermocouple voltage. For the exemplary embodiment shown, the current may vary proportionally to the voltage applied to the input pin 307. For a specific example, if the voltage produced by the thermocouple increases by 1 mV, then the current increases by 0.1 mA. Accordingly, the first signal converter 235 superimposes or shapes a signal on to the current provided from the controller 240. That is, the same power signal used to power the amplifier 306 is used to carry a signal functionally related to the thermocouple voltage. By superimposing the signal of the thermocouple voltage on to the current, only two terminals are required for connecting the first signal converter 235 to the controller 240. Consequently, the first signal converter 235 may “trick” the controller 240 into believing the first signal converter 235 is connected to an optical sensor. By “tricking” the controller 240, the thermocouple 230 and first signal converter 235 may be retrofitted with the controllers of the prior art.

[0029] Referring again to FIG. 5, the first and second output terminals 310 are connected to the third and fourth input terminals 320 and 330 of the second signal converter 265. The second signal converter 265 includes the first and second input terminals 320 and 330, one or more power terminals to receive a power from a source Vcc (e.g., 5 VDC), resistor R101, reference voltage source 335, differential amplifier 340, filter 345, and scaler 350.

[0030] The voltage source Vcc provides power to the first signal converter 235 via resistor R101 and output terminal 320. As was discussed above, the first signal conditioner 235 superimposes a signal on to the current of the power provided to the first signal conditioner. The varying current develops a varying voltage drop across resistor R101. The varying voltage drop results in a voltage signal proportional to the varying current and, consequently, is functionally related to the thermocouple voltage. The varying voltage developed across resistor R101 (also referred to a first voltage) is provided to the differential amplifier 340.

[0031] The differential amplifier 340 also receives a reference voltage from the reference voltage source 335. The differential amplifier 340 compares the varying voltage developed across resistor 101 with the voltage provided by the reference voltage source 335, and generates a second or difference voltage proportional to the difference of the two voltages. The second voltage is provided to the filter 345, which filters noise from the difference voltage and attenuates flame “flicker” effects. The filtered difference voltage is provided to a scaler 350. The scaler 350 scales the voltage to a desired voltage scale (e.g., 0-5 VDC), and provides the scaled voltage (also referred to as the “conditioned” voltage) to the processing unit 270 for analysis.

[0032] The memory 275 includes one or more software modules having instructions, and the processing unit 270 retrieves, interprets, and executes the instructions of the one or more software modules to control the burner assembly 130. In one embodiment of the invention, the processing unit 270 is a PIC16C74 microcontroller manufactured by Microchip Technology. However, other microcontrollers may be used in the invention. In addition, the processing unit 270 may alternatively be constructed with other analog and/or digital logic circuitry, and may include integrated and/or discrete circuit elements. Furthermore, the controller 240 may include other processing units for controlling other aspects of the paving machine 100, and the processing unit 270 and/or the controller 240 may include other elements (e.g., one or more analog-to-digital converters, one or more drivers, one or more power supplies, etc.) that would be apparent to one skilled in the art from the description contained herein.

[0033] The input device 250 provides an interface between the operator and the controller 240, and allows an operator to provide inputs to the controller 240. Of course the input device 250 may be multiple input devices, and may be part of a large interface that allows the operator to control the paving machine 100. Example input devices 250 include switches, levers, dials (including wheels), knobs, push buttons (including keyboards and keypads), pedals, touch devices (including touch screens) and other similar input devices.

[0034] The output device 255 provides an interface between the controller 240 and the operator, and allows the controller 240 to provide outputs to the operator. For example, the output device 255 may be able to provide an alarm to the operator upon receiving an alarm signal. Of course the output device 255 may be multiple output devices, and may be part of a large interface that allows the paving machine 100 to communicate with the operator. Example output devices 255 include display lights (including light-emitting diodes, incandescent bulbs, discharge lamps, fluorescent bulbs, etc.), display screens (including touch screens, LCDs, etc.), and sound devices (e.g., a speaker, tone generating devices, buzzers, etc.).

[0035] In operation, an operator activates the paving machine 100, and a power is provided to the controller 240. Upon receiving power, the processing unit 270 performs appropriate initialization operations, and obtains, interprets, and executes the one or more software modules from the memory 275. The operator controls the paving machine by providing inputs to the one or more input devices 250 as is known in the art. For example, the operator may activate a switch resulting in the paving machine 100 paving a bed.

[0036] As noted above the machine 100 shapes the parts material. During the shaping process, the screed plate 150 is controllably heated to a temperature that optimally heats the paving material for shaping. To heat the heating chamber 155, and consequently the screed plate 150, the controller 240 provides a signal to the blower 200, and to the fuel injection system 205 that results in a mixture of fuel and air being introduced into the combustion chamber 155. The controller 240 also provides a signal to the igniter 220 that results in ignition of the air/fuel mixture.

[0037] The controller 240 receives a chamber temperature signal having a relationship to the temperature of the heating chamber 155, and a thermocouple voltage having a relationship to the temperature surrounding the thermocouple junction 260 (i.e., the temperature of the expected flame path 162). The thermocouple voltage is provided to the first signal converter 235, which receives a current form the controller 240, and produces a signal superimposed on the current. The controller analyzes the signal that is superimposed on the current. For the embodiment shown, the second signal converter 265 converts the current signal into a first voltage, compares the first voltage with a reference voltage, and scales the difference signal to a desired scale. The resulting scaled voltage (also referred to as the conditioned voltage) is functionally related to the temperature surrounding the thermocouple junction 260, and is provided to the processing unit 270 for analysis. The processing unit controls the air/fuel mixture to provide a desired temperature, and an optimal burn consistency based on the inputs received from the input device, the temperature of the chamber, and the temperature of the expected flame path 162.

[0038] The signal provided by the thermocouple may indicate that the air/fuel mixture has not been ignited or has extinguished. If the fuel is not properly ignited, the controller 240 generates an output. The output may be provided to the fuel valve 210 that results in closure of the fuel valve 210. The output may also be provided to the one or more output devices 255 to generate an audio or visual alarm.

[0039] For one embodiment, the conditioned signal is sampling at a sampled rate (e.g., 30 msec), and is analyzed at an analysis rate (e.g., 1 sec) for determining whether the air/fuel mixture is lit. An exemplary embodiment for performing sampling is shown in FIG. 6, and an exemplary embodiment for performing analysis to determine whether the flame is lit is shown in FIG. 7. For the embodiment described, a flame analysis rate of 1 second has been found to be suitable because it corresponds to the thermal time constants of the paving machine 100.

[0040] As shown in FIG. 6, the processing unit 270 acquires a sample (block 500), and determines whether the burner assembly 130 is in the process of igniting the air/fuel mixture (block 505). The processing unit 270 does not utilize samples acquired during the ignition process because a large amount of noise is created during ignition of the air/fuel mixture. If the burner assembly 130 is in the process of igniting the air-fuel mixture, then the processing unit 170 exits the sampling subroutine.

[0041] If the burner assembly 130 is not in the process of igniting the system, then the software proceeds to analyze the sample. Specifically, the software 270 determines whether the sampled value is greater than a filtered value (block 510). If the sampled value is greater than the filter value, then the software determines that the conditioned signal is increasing and proceeds to block 515. Otherwise, the software proceeds to block 520.

[0042] At block 515, the software determines whether a trend_increasing_flag variable or object is set to true. The trend_increasing_flag variable informs the software whether the conditioned signal was previously determined to have an increasing trend. If the trend_increasing_flag variable is false (i.e., the trend of the conditioned signal was previously decreasing), then the software sets the trend_increasing_flag variable to true, sets a trend_decreasing_flag variable to false, and resets a trend_increasing_counter variable (block 525). The trend_increasing_counter variable is a counter that counts the number of increasing trend increments that have occurred without interruption (i.e., without a decrement). The software then increments the trend_increasing_counter variable, increases the filter value by an amount (block 530), and exits the sampling subroutine.

[0043] At block 525, the software determines whether the sampled value is less than the filter value. If the sampled value is less than the filter value, then the software determines that the conditioned signal is decreasing and proceeds to block 535. Otherwise, the software determines the conditioned signal is unchanged and exits the sampling subroutine.

[0044] At block 535, the software determines whether a trend_decreasing_flag variable is true. The trend_decreasing_flag variable informs the software whether the conditioned signal was previously determined to have a decreasing trend. If the trend_decreasing_flag variable is set to false (i.e., the trend of the conditioned signal was previously increasing), then the software sets the trend_decreasing_flag variable to true, sets the trend_increasing_flag variable to false, and resets a trend_decreasing_counter variable (act 540). The trend_decreasing_counter variable is a counter that counts the number of decreasing trend increments that have occurred without interruption (i.e., without a decrement). The software then increments a trend_decreasing_counter variable, decreases the filter value by an amount (block 545), and exits the sampling subroutine. Of course, in other embodiments, only one trend counter may be used.

[0045] The software continuously performs the sampling routine while the fuel valve 210 is open. In addition to performing the sampling routine, the software analyzes the flags and counters to determine whether the air-fuel mixture is lit. For one embodiment and as shown in FIG. 7, the software compares the current filter value with a previous_filter_value variable (block 550) to determine if the difference is greater than a threshold (block 555). If the difference between the two values is greater than a threshold, then a no_flame_flag variable is set to true (block 560). Otherwise, the no_flame_flag variable is set to false (block 565). For the embodiment shown, a decreasing thermocouple voltage signifies an increasing temperature, and an increasing thermocouple voltage signifies a decreasing temperature. If the difference is smaller than a threshold, the software determines that the air-fuel mixture is lit (i.e., the flame is on). If it is larger than the threshold, then the software determines that the air-fuel mixture is not lit (i.e., the flame is extinguished).

[0046] In addition to determining whether the difference between the current and previous filter values is greater than a threshold, the software analyzes the trend of the sampled values to determine whether the air/fuel mixture is not lit. Specifically, if the trend_increasing_flag variable is true (block 570), then the software determines whether the trend_increasing_counter variable is greater than a first value signifying a significant increasing trend (block 575). If the trend_increasing_counter variable is greater than a first value, then the software sets no_flame_flag variable to true (block 580). If the trend_decreasing_flag variable is true (block 585), then the software determines whether the trend_decreasing_counter variable is greater than a second value signifying a significant decreasing trend (block 590). If the trend_decreasing_counter variable is greater than a second value, the software sets no_flame_flag variable to true (block 595).

[0047] At block 600, the software analyzes no_flame_flag variable. If no_flame_flag variable is true, then the software generates an output (block 605) signifying the air-fuel mixture is not lit. The output may be used to close the fuel valve 210, and/or to provide an alarm to the operator with the one or more output devices 255. Otherwise, the software sets previous_filter_value to the current filter value (block 610), and returns from the analysis subroutine.

[0048] As can be seen from the above, the invention provides, among other things, a new and useful burner assembly 130 for heating a screed plate 150 connected to a frame 105 of a paving machine 100. Various features and advantages of the invention are set forth in the following claims.

Claims

1. A burner assembly for heating a screed plate of a screed assembly connected to a frame of a paving machine, the screed assembly including a heating chamber adjacent to the screed plate, the burner assembly comprising:

a blower that moves air into the heating chamber;

a fuel injection system including a fuel valve, the fuel injection system introducing fuel to the heating chamber;

an igniter that ignites the fuel to produce a flame;

a thermocouple having a junction positioned within an expected flame path, the thermocouple generating a thermocouple voltage having a relationship to a temperature surrounding the junction; and

a controller connected to the thermocouple, the controller operating the fuel valve based in part on the thermocouple voltage.

2. A burner assembly as set forth in claim 1 wherein the burner assembly further comprises a signal converter that receives the thermocouple voltage, and generates a signal simulating an optical sensor signal, and wherein the controller operates the fuel valve based in part on the signal simulating the optical sensor signal.

3. A burner assembly as set forth in claim 1 wherein the burner assembly further comprises a signal converter that receives the thermocouple voltage and a current from the controller, and superimposes a signal produced by the thermocouple voltage on to the current, and wherein the controller operates the fuel valve based in part on the superimposed signal.

4. A burner assembly as set forth in claim 1 and wherein the controller further operates the blower based in part on the thermocouple voltage.

5. A burner assembly as set forth in claim 1 wherein the burner assembly further comprises a signal converter electrically connected between the thermocouple and the controller, and wherein the signal converter receives the thermocouple voltage, receives a current from the controller, and controls an amplitude of the current based in part on the received thermocouple voltage.

6. A burner assembly as set forth in claim 5 wherein the signal converter includes an amplifier having a first input pin that receives the thermocouple voltage, and a first power pin that receives the current from the controller.

7. A burner assembly as set forth in claim 6 wherein the signal converter further includes a first resistor, and a second resistor, wherein the amplifier further includes a second input pin, a second power pin, and an output pin, wherein a first end of the first resistor is connected to the second input pin, and the output terminal, wherein the second end of the first resistor is connected to a ground, wherein a first end of the second resistor is connected to the first input pin, and wherein a second end of the second resistor is connected to the ground.

8. A burner assembly as set forth in claim 5 wherein the burner assembly further comprises a second signal converter electrically connected between the first signal converter and the controller, wherein the second signal converter provides the current to the first signal converter, and produces a conditioned voltage having a relationship to the amplitude of the controlled current.

9. A burner assembly as set forth in claim 5 wherein the second signal converter includes

a resistor having first and second ends, the first end being connectable to a power source, and the second end being connected to the first signal converter,

a differential amplifier having a first input connected to the second end of the resistor, and a second input connected to a reference voltage, and

an amplifier connected to the differential amplifier.

10. A burner assembly as set forth in claim 5 wherein the controller includes

a second signal converter connected to the first signal converter, the second signal converter providing the current to the first signal conditioner and producing a conditioned voltage having a relationship to the amplitude of the controlled current, and

a processing unit connected to the second converter, the processor receiving the conditioned voltage, executing one or more software modules to analyze the conditioned voltage, and producing an output to control the fuel valve based in part on the analyzed conditioned voltage.

11. A burner assembly as set forth in claim 10 wherein the second signal converter includes

a resistor having first and second ends, the first end being connected to a power source, and the second end being connected to the first signal converter,

a differential amplifier having a first input connected to the second end of the resistor, and a second input connected to a reference voltage, and

an amplifier connected to the differential amplifier.

12. A burner assembly as set forth in claim 1, a temperature sensor that senses a temperature of the heating chamber, and generates a chamber temperature signal, and wherein the controller further operates the fuel valve based in part on the chamber temperature signal.

13. A burner assembly as set forth in claim 12 wherein the controller further operates the blower based in part on the chamber temperature signal.

14. A burner assembly as set forth in claim 1 wherein the controller further comprises a signal conditioner that receives the thermocouple voltage, and produces a conditioned voltage having a scaled range, and wherein the controller operates the fuel valve based in part on the conditioned voltage.

15. A paving machine comprising:

a frame;

a hopper connected to the frame;

a screed assembly connected to the frame, the screed assembly including a screed plate and a heating chamber adjacent to the screed plate; and

a blower that moves air into the heating chamber,

a fuel injection system including a fuel valve, the fuel injection system introducing fuel to the heating chamber,

an igniter that ignites the fuel to produce a flame,

a thermocouple having a junction positioned within an expected flame path, the thermocouple generating a thermocouple voltage having a relationship to a temperature surrounding the junction, and

a controller connected to the thermocouple, the controller operating the fuel valve based in part on the thermocouple voltage.

16. A paving machine as set forth in claim 15 wherein the paving machine further comprises a signal converter that receives the thermocouple voltage, and generates a signal simulating an optical sensor signal, and wherein the controller operates the fuel valve based in part on the signal simulating the optical sensor signal.

17. A paving machine as set forth in claim 15 wherein the paving machine further comprises a signal converter that receives the thermocouple voltage and a current from the controller, and superimposes a signal produced by the thermocouple voltage on to the current, and wherein the controller operates the fuel valve based in part on the superimposed signal.

18. A paving machine as set forth in claim 15 and wherein the controller further operates the blower based in part on the thermocouple voltage.

19. A paving machine as set forth in claim 15 wherein the paving machine further comprises a signal converter electrically connected between the thermocouple and the controller, and wherein the signal converter receives the thermocouple voltage, receives a current from the controller, and controls an amplitude of the current based in part on the received thermocouple voltage.

20. A paving machine as set forth in claim 19 wherein the signal converter includes an amplifier having a first input pin that receives the thermocouple voltage, and a first power pin that receives the current from the controller.

21. A paving machine as set forth in claim 20 wherein the signal converter further includes a first resistor, and a second resistor, wherein the amplifier further includes a second input pin, a second power pin, and an output pin, wherein a first end of the first resistor is connected to the second input pin, and the output terminal, wherein the second end of the first resistor is connected to a ground, wherein a first end of the second resistor is connected to the first input pin, and wherein a second end of the second resistor is connected to the ground.

22. A paving machine as set forth in claim 19 wherein the paving machine further comprises a second signal converter electrically connected between the first signal converter and the controller, wherein the second signal converter provides the current to the first signal converter, and produces a conditioned voltage having a relationship to the amplitude of the controlled current.

23. A paving machine as set forth in claim 24 wherein the second signal converter includes

a resistor having first and second ends, the first end being connectable to a power source, and the second end being connected to the first signal converter,

a differential amplifier having a first input connected to the second end of the resistor, and a second input connected to a reference voltage, and

an amplifier connected to the differential amplifier.

24. A paving machine as set forth in claim 19 wherein the controller includes

a second signal converter connected to the first signal converter, the second signal converter providing the current to the first signal conditioner and producing a conditioned voltage having a relationship to the amplitude of the controlled current, and

a processing unit connected to the second converter, the processor receiving the conditioned voltage, executing one or more software modules to analyze the conditioned voltage, and producing an output to control the fuel valve based in part on the analyzed conditioned voltage.

25. A paving machine as set forth in claim 24 wherein the second signal converter includes

a resistor having first and second ends, the first end being connected to a power source, and the second end being connected to the first signal converter,

a differential amplifier having a first input connected to the second end of the resistor, and a second input connected to a reference voltage, and

an amplifier connected to the differential amplifier.

26. A paving machine as set forth in claim 15, a temperature sensor that senses a temperature of the heating chamber, and generates a chamber temperature signal, and wherein the controller further operates the fuel valve based in part on the chamber temperature signal.

27. A paving machine as set forth in claim 26 wherein the controller further operates the blower based in part on the chamber temperature signal.

28. A burner assembly as set forth in claim 15 wherein the controller further comprises a signal conditioner that receives the thermocouple voltage, and produces a conditioned voltage having a scaled range, and wherein the controller operates the fuel valve based in part on the conditioned voltage.

29. A temperature sensing circuit connectable to a power source comprising:

a thermocouple that produces a thermocouple voltage; and

a signal converter that receives the thermocouple voltage and a current from the power source, and superimposes a signal created by the thermocouple voltage on to the current.

30. A temperature sensing circuit as set forth in claim 29 wherein the signal converter includes an amplifier having a first input pin that receives the thermocouple voltage, and a first power pin that receives the current, and wherein the amplifier controls the amplitude of the current with a relationship to the thermocouple voltage.

31. A temperature sensing circuit as set forth in claim 30 and further comprising a resistor having a first end connected to a power supply, and a second end connected to the amplifier at the first power pin, and wherein the resistor receives the current, and develops a first voltage at the second end.

32. A temperature sensing circuit as set forth in claim 31 wherein the amplifier further includes a second input pin, a second power pin, and an output pin, wherein the second power pin is connected to a ground, and wherein the temperature sensing circuit further comprises:

a second resistor having a first end connected to the output pin, and the second input pin, a second end connected to the ground; and

a third resistor including a first end connected to the first input pin and a second end connected to a ground.

33. A temperature sensing circuit as set forth in claim 32 and further comprising:

a capacitor having a first end connected to the first power pin and a second end connected to ground.

34. A temperature sensing circuit as set forth in claim 31 and further comprising:

a differential amplifier having a first input connected to the second end of the first resistor, and a second input connected to a reference voltage, the differential amplifier receiving the first voltage and producing a second voltage proportional to the difference between the first voltage and the reference voltage; and

an amplifier connected to the differential amplifier that produces a third voltage proportional to the second voltage.

35. A temperature sensing circuit as set forth in claim 34 and further comprising:

a processing unit connected to the amplifier, the processing unit being operable to receive the third voltage, and to execute one or more software modules for analyzing the third voltage.

36. A method of controlling a burner assembly connected to a paving machine having a screed plate, the method comprising:

providing a thermocouple having a thermocouple junction;

positioning the thermocouple junction within an expected flame path;

opening a fuel valve to allow a fuel to flow through the valve;

igniting the fuel to produce a flame;

generating a signal functionally related to a temperature surrounding the thermocouple junction;

analyzing the thermocouple voltage; and

generating an output when the analyzed thermocouple voltage signifies a non-lit fuel condition.

37. A method as set forth in claim 36 and further comprising controllably heating the screed plate with the flame based in part on the analyzed thermocouple voltage.

38. A method as set forth in claim 36 wherein the generating a thermocouple voltage includes

providing an amplifier,

providing the thermocouple voltage to the amplifier,

providing a current to the amplifier,

controlling the amplitude of the current with the amplifier, the amplitude of the current being functionally related to the thermocouple voltage.

39. A method as set forth in claim 36 wherein analyzing the thermocouple voltage includes:

conditioning the thermocouple voltage to produce a conditioned voltage,

sampling the conditioned voltage to create a conditioned value,

providing a filtered value,

comparing the conditioned voltage to the filtered value,

increasing the filtered value when the conditioned value is greater than the filtered value,

decreasing the filtered value when the conditioned value is less than the filtered value.

40. A method as set forth in claim 39 wherein analyzing the thermocouple voltage further includes comparing the filtered value to a threshold value signifying a non-lit fuel condition.

41. A method as set forth in claim 39 wherein analyzing the thermocouple voltage further includes, when the conditioned value is greater than the filtered value,

setting a first flag,

incrementing a first counter, and

periodically comparing the first counter with a threshold counter value.

42. A method as set forth in claim 41 wherein analyzing the signal further includes, when the conditioned value is less than the filtered value,

setting a second flag,

incrementing a second counter,

periodically comparing the first counter with a second threshold counter value.

43. A method as set forth in claim 41 wherein the first and second counters are the same, and wherein the first and second threshold counter values are the same.

44. A method as set forth in claim 36 and further comprising:

closing the fuel valve when an output is generated signifying a non-lit fuel condition.

45. A method as set forth in claim 36 wherein the burner assembly includes a blower, and wherein the method further comprises:

deactivating the blower when an output is generated signifying a non-lit fuel condition.

46. A method as set forth in claim 36 wherein the burner assembly includes an alarm, and wherein the method further comprises:

generating an alarm when an output is generated signifying a non-lit fuel condition.